All Bomb Defuse quests should work like this:- Go to Side Quest (Green Bomb) Location- Reach the Designated Destination- Defuse all 3 bombs without Detected*- Escape the Area to complete

When you reach the destination, there will have some enemies moving around, try to defuse all bomb without spotted by anyone. If you spotted by a enemy, you have to disarm the remaining bomb within time limit (mostly 60 seconds) and escape after that to complete the mission. (You don't have to kill all enemies to finish, just leave)

For this kind of mission, if you are using bow or a sniper rifle (with suppressor), it shouldn't be a difficult task as long as you are not detected by a enemy, just disarm all bombs and then leave the area to complete it.